Fluid bearing

Also called Fluid Dynamic Bearings, Fluid Bearings are used in high speed or high precision applications where ordinary ball bearings may cause noise, vibration or accoustics. Noise and vibration from ball bearings occur either from the difficulty of making perfectly round bearings to a tight tolerance, or in high speed applications where the speed of the bearing will cause deformation in the ball bearings, and the resulting posibility of noise and vibration.

Fluid Bearings use a thin layer of oily substance sealed around the rotating shaft. The speed of rotation of the shaft causes hydrostatic effects that tend to keep the shaft centered in the casing and smooth vibration and noise (accoustics).

Hard drives manufactured with fluid bearings have noise ratings for bearings/motors on the order of 20-24 dB, where the threshold for human hearing is around 25 dB.